The present invention relates to target tracking and, in particular, it concerns a system and method for automatically acquiring a target with a narrow field-of-view gimbaled imaging sensor.
In warfare, there is a need for defensive systems to identify incoming threats and to automatically, or semi-automatically, operate appropriate countermeasures against those threats. Recently, in view of ever increasing levels of terrorist activity, there has also developed a need for automated missile defense systems suitable for deployment on civilian aircraft which will operate anti-missile countermeasures automatically when needed.
A wide range of anti-missile countermeasures have been developed which are effective against various different types of incoming threat. Examples of countermeasures include radar chaff and hot flare decoy dispenser systems, infrared countermeasure systems, and anti-missile projectile systems. Examples in the patent literature include: U.S. Pat. No. 6,480,140 to Rosefsky which teaches radar signature spoofing countermeasures; U.S. Pat. No. 6,429,446 to Labaugh and U.S. Pat. No. 6,587,486 to Sepp et al. which teach IR laser jamming countermeasures; U.S. Pat. No. 5,773,745 to Widmer which teaches chaff-based countermeasures; and U.S. Pat. No. 6,324,955 to Andersson et al. which teaches an explosive countermeasure device.
Of most relevance to the present invention are directional countermeasures, such as Directional IR Countermeasures (DIRCM), which must be directed accurately towards an incoming threat. For this purpose, such systems typically use a target-tracking subsystem with a narrow field-of-view (“FOV”) imaging sensor to track the incoming target. Typically, this may be a FLIR with an angular FOV of less than 10°.
In order to reliably detect incoming threats, automated countermeasure systems need to have a near-panoramic target-detection subsystem covering a horizontal FOV of at least 180°, and more preferably 270° or even 360°. Similarly, a large vertical FOV is also required, preferably ranging from directly below the aircraft up to or beyond the horizontal. For this purpose, a number of scanning or staring sensors are preferably combined to provide continuous, or pseudo-continuous, monitoring of the effective FOV.
In operation, the target-detection subsystem identifies an incoming target and, based upon the pixel position on the target-detection sensor which picks up the target, determines a target direction vector. A gimbal mechanism associated with the target-tracking sensor is then actuated to align the target-tracking sensor towards the target for tracking, target verification and/or countermeasure deployment.
In practice, the hand-off between the target-detection subsystem and the target-tracking subsystem is often unreliable. Specifically, the very large FOV of the target-detection sensors necessarily requires that the angular resolution of each target-detection sensor is very much lower than that of the target-tracking sensor. The physical limitations imposed by the low resolution detection data are often exacerbated by imprecision in mounting of the subsystems, flexing of the underlying aircraft structure during flight, and other mechanical and timing errors. The overall result is that the alignment error of the target-tracking subsystem relative to the target detected by the target-detection subsystem may interfere with reliable acquisition of the target, possibly preventing effective deployment of the countermeasures.
There is therefore a need for a system and method for automatically acquiring a target with a narrow field-of-view gimbaled imaging sensor which would achieve enhanced reliability of hand-off from the target-detection subsystem.